The medical industry has desired to accurately measure the strength of a healing wound in tissue for a variety of reasons. With recent new interest in cytokines, growth factors, and fetal regeneration, biomechanical studies of wound healing and tissue strength are becoming increasingly more important.
The test specimens for such wound healing tests are laboratory animals, most typically rats. Conventionally, a cut or incision is made on the animal, such as on the abdominal area, and the wound is permitted to heal for a certain time, typically a number of days. The pelt or skin area around the wound is then carefully excised and the excised area mounted in a vise-like device. This device, called an Instron tensiometer, then stretches the pelt transversely to the wound direction and the breaking strength of the wound is measured. Unfortunately, this method introduces a number of factors tending to degrade the accuracy and usefulness of the test as the wound must be excised and measured in vitro or outside of the body. For example, upon excision the pelt begins decomposition effecting its biomechanical properties and the excising and handling of the pelt introduce stresses which may affect the strength and sometimes even rupture relatively new wounds.
Another conventional in vitro method of wound strength testing is performed using an air insufflated positive pressure device. However, this method also requires that the pelt be excised. In this method the excised pelt is mounted between rings often with a thin elastic diaphragm behind it and is subjected to positive pressure until the wound ruptures. Again, since the wound area is excised and manipulated extensively, a great amount of error is introduced into the test.
While these methods have produced generally acceptable rupture strength results for wounds which have healed for several days, the error introduced is unacceptable on fragile and recent wounds and often significantly obscures the results of tests on wounds imparted less than a few days before testing and on fragile fetal wounds. Compounding the disadvantages of these in vitro methods is the fact that it is during the first few days after wounding when the wound is still quite fragile that many of the drugs for which the effects are being tested exhibit their most marked effect on wound healing. Further, since in vitro skin characterization methods require excision of the wound, subcutaneous attachments and fibrin deposits which contribute to wound strength are necessarily disrupted.
It would be desirable to test wounds with an increased accuracy and repeatability, particularly with respect to relatively recent and otherwise fragile wounds such as fetal wounds. It would also be desirable to measure biomechanical properties of skin in vivo, thus more closely measuring actual conditions when the skin is connected to subcutaneous material. It would be further desirable to measure biomechanical skin properties, such as elasticity, etc. without subjecting the specimen to the trauma of excising, thus even permitting limited biomechanical measurements, without rupture, on humans.